Gain control



Sept. 11, 1934. I 1 FiWHITlNG 1,973,453

GAIN CONTROL Filed July 22., 1929 a a9 Invemor Witness 97 W floazmz BY Mu L7 Patented Sept. 11, 1934 UNITED STATES Hi h PATENT or GAIN CONTROL New York Application July 22, 1929, Serial No. 380,200

6 Claims.

This invention relates to a new and improved device for adjusting the amplification of a multistage amplifier.

In previous systems the amplification was adjusted ahead of the first amplifier tube, which has the disadvantage of leaving all the stages in a condition sensitive to troubles caused by vibration, tube noises and acoustic feed-back. Another previous system employed, in addition to 10 the control ahead of the first tube, an auxiliary control between the first and second stages. This also has a disadvantage of producing clicks or disturbances due to irregularities in the sequences of inserting the large losses in the parl5 ticular type of control. In the proposed new form of control alternate or successive changes are made in front of, or between the stages of the amplifier, these changes being affected by the continuous turning of a single control dial. Two or more control points may be selected, such as in front of the first stage, between the first and second stages, the second and third stages, etc. One step is effected between two of these stages, the next step between the next two stages and so forth until a single cycle has been completed, at which point the process may repeat itself. This may be accomplishedby mounting the control potentiometer on the control switch in such a manner that the same knob turns all the brushes; and, by strapping the contact studs together in the proper manner or by using elongated contact studs properly arranged, stepping is accomplished in the proper sequence.

This method can be applied to gain control obtained in any of the well-known ways, such as the use of potentiometers with or without series resistance taps, or by use of transformer or retard coil, equipped with taps.

The main object of my invention is to provide a new gain control for amplifiers such that a plurality of stages may be controlled by one knob.

Another object of my invention is to provide a gain control for multi-stage amplifiers that will operate in a step by step manner in any predetermined sequence.

Another object of my invention is to provide a gain control for a multi-stage amplifier whereby the amplification between stages may be continuously adjusted over a range impractical to cover at a single interstage point.

It is also an object of my invention to provide a gain control for a multi-stage amplifier whereby the amplification of successive stages may be so controlled as to eliminate amplifier disturbances commonly found in previous methods of control.

Further objects and advantages will be apparent with reference to the accompanying drawing in which:

Figure 1, illustrates a possible method of construction, utilizing three stages of control. Potentiometers 1, 2 and 3 are mounted, as shown, on a suitable base 6, a shaft 4 of insulating mate rial, couples the three separate units. A knob '7 serves as a control for the system. Reference to Figure 2 will show further details of construction. This figure is a section taken through A--A of Figure 1. This knob '7 is secured by means of a set screw to the shaft 4. The mov able arm 5 is secured to the shaft 4 and makes contact with the studs 8 mounted on the potentiometer plate. The resistance unit 9 is mounted in back of the plate and taps are taken from 9 to make contact with the studs 8 in a manner to be described later. The View of section B-B of Figure 2 is shown in Figure 3. This shows a method or" strapping adjacent studs to effect a step by step control schedule. By changing the scheme of strapping of studs, any sequence of control can be obtained. The lead 10 is connected to the movable arm or brush 5. The other two connections to the potentiometer are shown at the extremities of the resistance 9 at 11 and 12.

A typical application of this staggered gain control is shown in Figure 4. A conventional three stage amplifier is shown. The plate circuits are not shown in full since the application of the gain control does not effect the same directly. A potentiometer is connected in parallel with the secondary 14 of the first amplifying transformer 13, and connections are made on the potentiometer at points 11 and 12.

The movable arm 5 makes contact through 10 to the grid 15 of the first amplifying tube 17. The following two stages have similar connections. A probable sequence of operation would be as follows: Starting with the movable arm 5 all on contact stud 11, all three stages would be set for a position of maximum gain. As the arm 5 is turned in a clockwise direction to the second contact stud, the second stage of amplification is efiected or the gain is decreased by the first step. Stages three and one are still at maximum gain, .105 due to the fact that the adjacent studs are strapped together. As the contact arm moves to the third stud, stage number three receives a change in gain by one step while two and one remain as before. Another contact step will efiect stage one.

The process here repeats itself starting with stage two, which will, on the next contact step, be effected by a second step of decreased gain.

Although only four steps in gain control are here shown, any number may be applied to this method. The sequence of operation was chosen as two, three, one, which necessarily does not limit the application to any other that may be practical.

A gain control of this type has the advantage of giving continuous control. efiects the gain of the amplifier due to successive amplification changes of the various stages. This makes the amplifier more free from interstage disturbances as would be present in the case of a single interstage control. The single interstage volume control requires nearly as many potentiometer resistances or coil taps as doesthe multi-stage control and has the disadvantage of a very limited range.

It is to be understood that thus having described a particular multiple staggered gain'control for the purpose of illustrating my invention, I do not desire to restrict myself, as various changes may be made without departing from the scope of the appended claims.

I claim:

1. In a gain control of the class described, a plurality of impedance units, a plurality of equally spaced contact studs connected to said impedance units, means including a unitary control for simultaneously engaging said contact studs to effect successive changes of impedance in said units, said contact studs being connected to said impedance units in staggered arrangement so that said impedance changes occur in only one unit at a time.

2. In a multi-stage amplifier having a plurality of audion tubes, a gain control comprising a plurality of variable impedance units connected across the input circuits ahead of and between said tubes, a plurality of equally spaced contact studs connected to each of said impedance units, a revoluble shaft, a plurality of contact arms mounted on said shaft, each associated with an input circuit of said tubes and adapted to simultaneously engage said single contact studs, means for rotating said shaft to successively engage said contact arms with said contact studs to Turning the knob '7 effect changes of impedance in said units, said contact studs being connected to said impedance units in such a manner so that the impedance changes occur in only one unit at a time.

3. In an amplifier having a plurality of audion tube stages, an impedance unit connected in the input circuit of each audion tube a plurality of contacts connected to said impedance units in staggered arrangement, a plurality of contact arms adapted to engage said contacts, and means for simultaneously moving said contact arms from one set of contacts to another for varying the impedance of said units singly to efiect a continuous variation of the over-all gain of said amplifier.

4. In an amplifier having a plurality of audion tube stages, a multiple stage gain control comprising a plurality of potentiometer impedance units connected in the input circuits of the audion tubes and having a staggered step contact point arrangement, and single control means'associated therewith operable at will for simultaneously actuating all of said units and for continuously varying the amplification in small steps ahead of simultaneously actuating all of said elements whereby the gain of said amplifier may be changed continuously without afiecting the'gain of more than one stage at a time.

6:111 an amplifier having a plurality of audion tube stages, a multiple stage gain control comprising a plurality of variable impedance units I connected across the input circuits betweenthe audion tubes and having a staggered step contact point arrangement, and means associated with said contacts having asingle control operable at of said units for continuously varying the overall gain of the amplifier in small steps by successive changes of impedance ahead of and between stages thereof.

DONALD FAIRFAX WHI'I ING.

will for simultaneously adjusting'the impedance 

